1. Technical Field
The present invention relates to the field of modem to modem data communication; and, more specifically, it relates to a modem to modem communication and three-way calling and call waiting telephony services. The present invention also relates to the initialization and reconnection of a V.90 modem system.
2. Description of Related Art
A conventional communication system typically establishes an Internet data session through a local and a remote ISP (Internet Service Provider) modem via a telephone switching network. Similarly, other modem to modem communication uses the telephone switching network as the communication link. Such modems often share a single telephone line with other local telephony devices, e.g., telephones, facsimile machines, answering machines, etc.
To handle multiple incoming calls, telephone switching networks offer three-way calling and call waiting services. Such services can be accessed through manual interaction of a person using a telephone. Telephone switching networks have also added caller identification (caller ID) services to support call waiting. Thus, the person using the telephone may view the caller ID before deciding to accept an incoming call during a ongoing telephone conversation.
To maintain a data session between modems, continuous modem connection must be maintained during the data session. If after a period of time the modem signaling is lost, modems will conclude that the data session has been terminated and will disconnect.
When a telephone call waiting tone (indicating the presence of caller ID) is detected during a local modem to remote modem data session, a decoding process involving both the local modem and a telephone switching network CO (Central Office) may be undertaken to retrieve the caller ID. During the caller ID decoding process, however, the remote modem usually disconnects. Thus, the remote modem must be redialed to reestablish and continue the data session.
If the local modem does not attempt to decode the caller ID, the call waiting signaling will, at a minimum, interfere with ongoing communication and may cause the modems to hang up or retrain. Thus, the telephone switching network provides a mechanism for turning on and off the call waiting service. Before beginning the modem to modem data session, the call waiting service is turned off for the duration of the session. However, doing so prevents a user from receiving any other incoming calls on a shared telephone line. As a result, users are forced to add dedicated telephone lines for each type of telephony device in their premises.
56 kbps modems are now standardized in accordance with the ITU V.90 Recommendation. However, many 56 kbps modems, particularly end user modems, may only be compatible with legacy modes such as K56flex, V.34, V.FC, and V.32. Such legacy modems, and downwardly compatible V.90 modems, may have an undesirably long connect or initialization time between dial-up and full rate data mode. The startup time can be up to 30 seconds, which can be rather annoying and unattractive from the perspective of the end user, especially in light of other data communication protocols that appear to operate in an “always connected” manner.
V.90 modems that support legacy modem protocols typically perform the functions shown in Table 1 during initialization. The time periods associated with the operations set forth in Table 1 may vary from connection to connection depending upon various factors such as the server speed and channel conditions.
TABLE 1Conventional V.90 Modem StartupPROTOCOLOPERATIONTIME (seconds)—Dialing1  —Call Establishment1  V.8bisCapabilities Exchange3.5V.8Capabilities Exchange3.5V.90 Phase 2Probing & Ranging1.5V.90 Phase 3Digital Impairment Learning;8.5Initial APCM TrainingV.90 Phase 4Final APCM Training;2.5Set Power Levels;Constellation TransmissionV.42/V.42bisError Correction;0.5Data Compression—Login0.5-5  TOTAL =22.5-27.0
The V.8bis operation includes a relatively long timeout period that encompasses much of the time period associated with the operation. This operation is described in detail in ITU-T Recommendation V.8bis (International Telecommunication Union, August 1996), the content of which is incorporated by reference herein. The V.8bis protocol is an extension of the V.8 protocol, as described in ITU-T Recommendation V.8 (International Telecommunication Union, February 1998), the content of which is incorporated by reference herein. In accordance with V.8bis and/or V.8, the two modem devices exchange their individual capabilities such that compatible protocols may be utilized during subsequent initialization and data communication procedures.
The various V.90 startup phases are utilized to determine the analog and digital channel characteristics, to train the modem equalizers, and to otherwise attempt to optimize the current communication session. The details of the V.90 startup phases and other aspects of a V.90 modem system may be found in ITU-T Recommendation V.90 (International Telecommunication Union, September 1998), the content of which is incorporated by reference herein. Although a portion of the V.90 startup segments shown in Table 1 are required without regard to the location or status of the client modem, many of the operations could be eliminated or shortened upon repeated connections associated with the same (or nearly identical) channel characteristics.
In a conventional V.90 modem system, error correction and data compression techniques are performed during the V.42/V.42bis stage. The specifics of V.42 are contained in ITU-T Recommendation V.42 (International Telecommunication Union, October 1996), the content of which is incorporated by reference herein. The specifics of V.42bis are contained in ITU-T Recommendation V.42bis (International Telecommunication Union, January 1990), the content of which is incorporated by reference herein. The V.42 operation is desirable such that the modem system can perform the login procedure in a substantially “error free” mode. The login procedure may be conducted with CHAP and PAP protocols; both are utilized for security purposes in the context of point-to-point protocol (“PPP”) connections, e.g., a connection between a client computer and an internet service provider server. From the perspective of the V.90 modem devices, the login information is transmitted as data. Once the login procedure is performed, the dial-up connection is complete and data may be transmitted between the server and the host software associated with the client.
The widespread use of the internet as a daily research, entertainment, and communication tool has increased the deployment of 56 kbps modems. However, many channels can only support legacy modes such as V.34. Thus, although most newer modems (particularly those sold with new personal computers) are compatible with the V.90 Recommendation, many legacy modes are still in use. The long initialization period associated with V.90 modems that fall back into legacy modes may be annoying and undesirable in many applications and can be a serious hindrance where a user would like to establish an immediate connection after an unanticipated disconnect. In addition, even in the context of a connection between two V.90 modem devices, the long V.90 startup phases may test the mettle of an impatient end user. Accordingly, it would be highly desirable to reduce the initialization time normally associated with a conventional V.90 modem system.
A given modem communication session may be interrupted or disconnected for any number of reasons. For example, a call waiting signal may disrupt a modem connection to the extent that the modem call must either be reconnected or reinitialized. As another example, it may be possible to place a current modem connection on hold to enable the user to answer an incoming call in response to a call waiting signal or to enable the user to place an outgoing call without disconnecting the modem connection. Ideally, the modem connection could be re-established in an instantaneous manner. However, in a practical system, a retraining or reinitialization procedure must be carried out to ensure that the two end devices are properly synchronized and to ensure that the channel is adequately equalized. As discussed above, conventional V.90 modem systems may spend more than 20 seconds during such retraining and reinitialization. Accordingly, it would also be desirable to reduce the reconnection time between the same modem devices in response to a temporary disconnect or a temporary pause in the data communication.
Further disadvantages of the related art will become apparent to one skilled in the art through comparison of the related art with the drawings and the remainder of the specification.